The present invention relates to absorbent articles, in particular sanitary napkins with improved comfort, particularly using breathable backsheets while maintaining protection level performance.
The development of absorbent articles, particularly catamenial products, are driven by two need of the consumer, protection and comfort.
One means for providing consumer comfort benefits in absorbent articles is by the provision of breathable products. Breathability has typically concentrated on the incorporation of so called xe2x80x98breathablexe2x80x99 in the absorbent articles. Commonly utilized breathable backsheets are microporous films and apertured formed films having directional fluid transfer as disclosed in for example U.S. Pat. No. 4,591,523. Both these types of breathable backsheets are vapour permeable allowing gaseous exchange with the environment. This thereby allows for evaporation of a portion of the fluid stored in the core and increases the circulation of air within the absorbent article. The latter is particularly beneficial as it reduces the sticky feeling experienced by many wearers during use, commonly associated with the presence of an apertured formed film or film like topsheet, particularly over extended periods of time. This is a result of topsheets designed to achieve a clean and dry appearance. These topsheets tend to be smooth thereby minimizing the build up of fluid on the surface of the topsheet. However, the benefits of a smooth textured surface are achieved at the expense of consumer comfort, particularly under hot and humid conditions.
However, the main drawback associated with the use of breathable backsheets in absorbent articles is the negative effect on the protection level performance, by leakage known as wet through onto the uses"" garment. Although, breathable backsheets in principle only allow the transfer of materials in the gaseous state, physical mechanisms such as extrusion, diffusion and capillary action may still occur and result in the transfer of the fluids from the absorbent core through the backsheet and onto the users"" garments. In particular, these mechanisms become more dominant if the product is utilised during physical exertion, or for heavy discharge loads or over extended periods of time. Thus, whilst the incorporation of breathable backsheets in absorbent articles is highly desirable from a comfort standpoint, since the primary role of a backsheet still remains the prevention of liquid leakage, such breathable backsheets cannot be satisfactorily incorporated into products.
The problem of wet through onto users"" garments due to the incorporation of such breathable backsheets in absorbent articles has indeed also been recognised in the art. Attempts to solve the problem have mainly resided in the use of multiple layer backsheets such as those illustrated in U.S. Pat. No. 4,341,216. Similarly European patent application no. 710 471 discloses a breathable backsheet comprising an outer layer of a gas permeable, hydrophobic, polymeric fibrous fabric and an inner layer comprising an apertured formed film having directional fluid transport. The backsheet construction preferably has no liquid transport/wet through under certain specified test conditions. Also European patent application no. 710 472 discloses a breathable backsheet consisting of at least two breathable layers which are unattached to one another over the core area. The backsheet construction preferably has no liquid transport/wet through under certain specified test conditions.
U.S. Pat. No. 4,713,068 discloses a breathable clothlike barrier for use as an outer cover for absorbent articles. The barrier comprises at least 2 layers, a first layer having a specified basis weight, fibre diameter and pore size and a second layer comprising a continuous film of poly (vinyl alcohol) having a specified thickness. The barrier also has a specified water vapour transmission rate and level of impermeability.
However, none of the above proposed solutions have been able to provide a fully satisfactory solution to the problem of breathable backsheet wet through under all conditions. Furthermore, another problem associated with the exemplified multi layer backsheets is an increase in total thickness of the product and a reduction in the flexibility, both of which result in a consumer noticeable reduction in product comfort.
An alternative proposed solution to the problem of breathable backsheet wet through relates to the improvement of the absorbent material such that little or no liquid comes into contact with the backsheet, thereby preventing wet through. This is typically achieved by increasing the amount of absorbent material in the article. However, this results in an absorbent article which is extremely thick which is highly undesirable from a consumer comfort standpoint. Hence, the absorbent article whilst having the required protection level and still maintaining some comfort benefits by the presence of the breathable backsheet, suffers from a lack of comfort from a different source, in this case the increased dimensions of the article.
In addition the above solution also results in a reduction in the flexibility of the article, particularly evident as an increase in the cross section stiffness. It is however also well established that in order to be comfortable for the wearer absorbent articles need to be cross sectionally flexible. It is believed that the more cross sectionally flexible an absorbent article is, the less will it be noticeable to the wearer. Thus flexibility is another highly desirable comfort requirement of modern absorbent articles.
EPO 705 583 and EPO 705 584 propose longitudinally flexible absorbent articles which are vapour permeable. However, the exemplified absorbent articles are typically very thin and do not address the absorbency capacity of the article or the problem of wet through.
Thus it not currently possible to provide a comfort improvement to absorbent articles such as by the incorporation of breathable backsheet, without negatively impacting protection levels. In the alternative, if the result of protection level problem is then addressed either by using a multi layered backsheet or increasing the thickness of the core, there is a further negative impact on the comfort level of the article and vice versa.
Consequently, as the incorporation of breathable backsheets in absorbent articles results in reduction of the protection level, further desirable product comfort modifications such as reducing the thickness of the product and improving the flexibility of the product which would further acerbate the problem may not be incorporated in the absorbent article.
Thus, there exists a dichotomy in the means available to provide increased consumer comfort in absorbent products and acceptable protection levels. It is therefore an objective of the present invention to provide an absorbent article having improved comfort which maintains an acceptable level of protection.
It has now been found that this objective may be achieved by the provision of an article whose individual elements must meet certain key functional parameter criteria in terms of comfort provision and/or protection such as the backsheet wet through/liquid permeability, the topsheet dryness, the core caliper and core vapour or vapour/air permeability. Furthermore, these elements are combined such that the resultant product, in addition to these individual elements, meets overall criteria such that it has a certain dryness index and sensory index. The present invention has identified the key components which affect the principle comfort requirements of flexibility, breathability, dryness and caliper and the key components of protection such as liquid retention/wet through and rewet. Surprisingly, it has been found that the specfic combination of these components, provides an article delivering both high protection levels as well as high comfort to the consumer. In particular it is believed that breathability must be considered in terms of total article breathability in addition to the backsheet breathability in order to provide a truly breathable product.
A further advantage of the present invention is that one individual low performing component of the absorbent article in terms of rewet, wet through or caliper, but still within the component range, may be compensated by the high performance of another component provided that the overall product criteria are still met.
According to the present invention, each component layer is joined so as to minimise the impact on the product criteria parameters. Thus, a further aspect of the present invention relates to the method of manufacture of the absorbent article.
The present invention relates to a disposable absorbent article comprising a liquid pervious topsheet, a breathable backsheet, and an absorbent core. The absorbent core has a caliper of less that 12 mm and is positioned intermediate the liquid pervious topsheet and the breathable backsheet. The liquid pervious topsheet, absorbent core, and breathable backsheet comprise at least one layer. The topsheet has a liquid retention of less than 0.22 g for a 2.0 g load in the topsheet liquid retention test. The absorbent core has a vapour permeability of at least 200 g/m2/24 hrs. as defined in the vapour permeability test. The breathable backsheet has a liquid permeability of less than 0.16 g for a 15 ml. load as defined in the liquid permeabilty test. The liquid pervious topsheet, absorbent core, and breathable backsheet are joined such that the absorbent article has a dryness index of greater than 0.5 and a sensory index of greater that 50.
The present invention relates to absorbent disposable articles such as sanitary napkins, panty liners, incontinence products and baby diapers. Typically such products comprise the elements of a liquid pervious topsheet, a backsheet and an absorbent core intermediate said topsheet and said backsheet. According to the present invention the topsheet, backsheet and core may be selected from any of the known types of these components provided that they meet certain comfort and protection performance requirements detailed herein. In particular, the key performance criteria have been identified as: the topsheet liquid retention performance which gives an indication of the ability of the topsheet to maintain a dry surface and thereby keep the skin of the wearer dry; the permeability of the absorbent core and its thickness which relate to the absorbent capacity of the core and it ability to allow the flow of vapour and/or air through it and the backsheet wet through/liquid permeability which indicates the ability of the breathable backsheet to retain the absorbed fluid. Furthermore, the individual elements are joined, preferably utilising optimised joining techniques such that the final product also meets specific comfort and performance level criteria also described herein.
According to the present invention the absorbent article comprises as an essential component a topsheet. The topsheets suitable for use herein may be any topsheet known in the art.
The topsheets for use herein may comprise a single layer or a multiplicity of layers. In a preferred embodiment the topsheet comprises a first layer which provides the user facing surface of the topsheet and a second layer between the first layer and the absorbent structure/core. The topsheet typically extends across the whole of the absorbent structure and can extend into and form part of or all of the preferred sideflaps, side wrapping elements or wings.
The topsheet as a whole and hence each layer individually needs to be compliant, soft feeling, and non-irritating to the wearer""s skin. It also can have elastic characteristics allowing it to be stretched in one or two directions. As used herein the topsheet hence refers to any layer or combination of layers whose principle function is the acquisition and transport of fluid from the wearer towards the absorbent core.
According to the present invention the topsheet may be formed from any of the materials available for this purpose and known in the art, such as non woven fabrics, films or combinations of both. In a preferred embodiment of the present invention at least one of the layers of the topsheet comprises a liquid permeable apertured polymeric film. Preferably, the upper layer is provided by a film material having apertures which are provided to facilitate liquid transport from the wearer facing surface towards the absorbent structure, as detailed for example in U.S. Pat. Nos. 3,929,135, 4,151,240, 4,319,868, 4,324,426, 4,343,314 and 4,591,523.
According to the present invention the topsheets suitable for use herein must have a topsheet liquid retention of less than 0.22 g, preferably less than 0.15 g, more preferably less than 0.1 g, most preferably 0 g, as defined in the liquid retention test disclosed hereinafter.
The absorbent article according to the present invention also comprises a breathable backsheet. The backsheet primarily prevents the extrudes absorbed and contained in the absorbent structure from wetting articles that contact the absorbent product such as underpants, pants, pyjamas and undergarments thereby acting as a barrier to fluid transport. In addition however, the breathable backsheet of the present invention permits the transfer of at least vapour, preferably both vapour and air, through it and thus allows the circulation of gases into and out of the backsheet. The backsheet typically extends across the whole of the absorbent structure and can extend into and form part of or all sideflaps, side wrapping elements or wings.
According to the present invention any known breathable backsheet or multiple layer breathable backsheet composite may be used in the absorbent article provided that the backsheet meets the requirement of the liquid permeability test as defined herein. The breathable backsheets of the present invention have a liquid permeability at 15 ml. load of less than 0.16 g, preferably of less than 0.10 g, more preferably 0 g.
According to the present invention suitable breathable backsheets for use herein comprise at least one gas permeable layer. Suitable gas permeable layers include 2 dimensional, planar micro- and macro-porous films, macroscopically expanded films, formed apertured films and monolithic films. According to the present invention the apertures in said layer may be of any configuration, but are preferably spherical or oblong and may also be of varying dimensions. The apertures preferably are evenly distributed across the entire surface of the layer, however layers having only certain regions of the surface having apertures are also envisioned.
Suitable 2 dimensional planar layers of the backsheet may be made of any material known in the art, but are preferably manufactured from commonly available polymeric materials. Suitable materials are for example GORTEX or SYMPATEX materials well known in the art for their application in so-called breathable clothing. Other suitable materials include XMP-1001 of Minnesota Mining and Manufacturing Company, St. Paul, Minn., USA and Exxaire XBF-101W, supplied by the Exxon Chemical Company. As used herein the term 2 dimensional planar layer refers to layers having a depth of less than 1 mm, preferably less than 0.5 mm, wherein the apertures have an average uniform diameter along their length and which do not protrude out of the plane of the layer. The apertured materials for use as a backsheet in the present invention may be produced using any of the methods known in the art such as described in EPO 293 482 and the references therein. In addition the dimensions of the apertures produced by this method may be increased by applying a force across the plane of the backsheet layer (i.e. stretching the layer).
Suitable apertured formed films include films which have discrete apertures which extend beyond the horizontal plane of the garment facing surface of the layer towards the core thereby forming protuberances. The protuberances have an orifice located at its terminating end. Preferably said protuberances are of a funnel shape, similar to those described in U.S. Pat. No. 3,929,135. The apertures located within the plane and the orifices located at the terminating end of protuberance themselves maybe circular or non circular provided the cross sectional dimension or area of the orifice at the termination of the protuberance is smaller than the cross sectional dimension or area of the aperture located within the garment facing surface of the layer. Preferably said apertured preformed films are uni directional such that they have at least substantially, if not complete one directional fluid transport towards the core.
Suitable macroscopically expanded films for use herein include films as described in, for example, in U.S. Pat. No. 4,637,819 and U.S. Pat. No. 4,591,523.
Suitable monolithic films include HYTREL, available from DuPont Corporation, USA, and other such materials as described in Index 93 Congress, Session 7A xe2x80x9cAdding value to Nonwovensxe2x80x9d, J-C Cardinal and Y. Trouilet, Dupont de Nemours International S.A., Switzerland.
Preferred breathable backsheets for use herein are those having a high vapour exchange, most preferably both a high vapour and high air exchange.
According to the present invention the absorbent for use in herein may be selected from any of the absorbent core systems known in the art provided that certain requirements concerning caliper and vapour and/or air permeability as defined herein are met. As used herein the term absorbent core refers to any material or multiple material layers whose primary function is to absorb, store and distribute fluid. The absorbent core of the present invention has a vapour permeability of 200 g/m2/24 hrs, greater than 500 g/m2/s, preferably greater than 800 g/m2/24 hrs, most preferably 1200 g/m2/24 hrs., most preferably greater than 1500 g/m224 hrs. In a preferably embodiment of the present invention the absorbent core also has an air permeability of greater than 200 l/m2/s, more preferably greater than 800 l/m2/s, most preferably greater than 1200 l/m2/s. The absorbent core thus has a caliper of less that 12 mm, preferably less than 8 mm, more preferably less than 5 mm, most preferably from 5 mm to 2 mm.
According to the present invention, the absorbent core can include the following components: (a) an optional primary fluid distribution layer preferably together with a secondary optional fluid distribution layer; (b) a fluid storage layer; (c) an optional fibrous (xe2x80x9cdustingxe2x80x9d) layer underlying the storage layer; and (d) other optional components.
One optional component of the absorbent core according to the present invention is a primary fluid distribution layer and a secondary fluid distribution layer. The primary distribution layer typically underlies the topsheet and is in fluid communication therewith. The topsheet transfers the acquired fluid to this primary distribution layer for ultimate distribution to the storage layer. This transfer of fluid through the primary distribution layer occurs not only in the thickness, but also along the length and width directions of the absorbent product. The also optional but preferred secondary distribution layer typically underlies the primary distribution layer and is in fluid communication therewith. The purpose of this secondary distribution layer is to readily acquire fluid from the primary distribution layer and transfer it rapidly to the underlying storage layer. This helps the fluid capacity of the underlying storage layer to be fully utilized. The fluid distribution layers can be comprised of any material typical for such distribution layers.
Positioned in fluid communication with, and typically underlying the primary or secondary distribution layers, is a fluid storage layer. The fluid storage layer can comprise any usual absorbent material or combinations thereof. It preferably comprises absorbent gelling materials usually referred to as xe2x80x9chydrogelxe2x80x9d, xe2x80x9csuperabsorbentxe2x80x9d, hydrocolloidxe2x80x9d materials in combination with suitable carriers.
The absorbent gelling materials are capable of absorbing large quantities of aqueous body fluids, and are further capable of retaining such absorbed fluids under moderate pressures. The absorbent gelling materials can be dispersed homogeneously or non-homogeneously in a suitable carrier. The suitable carriers, provided they are absorbent as such, can also be used alone.
Suitable absorbent gelling materials for use herein will most often comprise a substantially water-insoluble, slightly cross-linked, partially neutralised, polymeric gelling material. This material forms a hydrogel upon contact with, water. Such polymer materials can be prepared from polymerizable, unsaturated, acid-containing monomers which are well known in the art.
Suitable carriers include materials which are conventionally utilized in absorbent structures such as natural, modified or synthetic fibers, particularly modified or non-modified cellulose fibers, in the form of fluff and/or tissues. Suitable carriers can be used together with the absorbent gelling material, however, they can also be used alone or in combinations. Most preferred are tissue or tissue laminates in the context of sanitary napkins and panty liners.
An embodiment of the absorbent structure made according to the present invention comprises a double layer tissue laminate formed by folding the tissue onto itself. These layers can be joined to each other for example by adhesive or by mechanical interlocking or by hydrogen bridge bands. Absorbent gelling material or other optional material can be comprised between the layers.
Modified cellulose fibers such as the stiffened cellulose fibers can also be used. Synthetic fibers can also be used and include those made of cellulose acetate, polyvinyl fluoride, polyvinylidene chloride, acrylics (such as ORLON), polyvinyl acetate, non-soluble polyvinyl alcohol, polyethylene, polypropylene, polyamides (such as nylon), polyesters, bicomponent fibers, tricomponent fibers, mixtures thereof and the like. Preferably, the fiber surfaces are hydrophilic or are treated to be hydrophilic. The storage layer can also include filler materials, such as perlite, diatomaceous earth, vermiculite, etc., to improve liquid retention.
If the absorbent gelling material is dispersed non-homogeneously in a carrier, the storage layer can nevertheless be locally homogenous, i.e. have a distribution gradient in one or several directions within the dimensions of the storage layer Non-homogeneous distribution can also refer to laminates of carriers enclosing absorbent gelling materials partially or fully.
An optional component for inclusion in the absorbent core according to the present invention is a fibrous layer adjacent to, and typically underlying the storage layer. This underlying fibrous layer is typically referred to as a xe2x80x9cdustingxe2x80x9d layer since it provides a substrate on which to deposit absorbent gelling material in the storage layer during manufacture of the absorbent core. Indeed, in those instances where the absorbent gelling material is in the form of macro structures such as fibers, sheets or strips, this fibrous xe2x80x9cdustingxe2x80x9d layer need not be included. However, this xe2x80x9cdustingxe2x80x9d layer provides some additional fluid-handling capabilities such as rapid wicking of fluid along the length of the pad.
The absorbent core according to the present invention can include other optional components normally present in absorbent webs. For example, a reinforcing scrim can be positioned within the respective layers, or between the respective layers, of the absorbent core. Such reinforcing scrims should be of such configuration as to not form interfacial barriers to fluid transfer. Given the structural integrity that usually occurs as a result of thermal bonding, reinforcing scrims are usually not required for thermally bonded absorbent structures.
Another component which can be included in the absorbent core according to the invention and preferably is provided close to or as part off the primary or secondary fluid distribution layer are odor control agents.
The potential benefits of incorporating a breathable backsheet into an absorbent structure have been extensively referred to in prior art but, a simple observation of available products in the market paces clearly points to a basic failure to realize a benefit in use. In many instances the problem has resulted from an inability to control through breathable backsheet wet-through. According to the present invention the absorbent elements meeting the requirements as described herein above must as an essential requirement be combined such that the resultant absorbent article product meets certain performance and comfort indexes herein referred to as the sensory index and the dryness index. The dryness index is a function of the effective breathability test and rewet test of the absorbent article and the sensory index is a function of the effective breathability test, flexibility and caliper of the absorbent article. The test methods are defined herein after. The indices are defined by the equations below:
Dryness index=Effective breathability/(Rewet test)
Sensory index=Effective breathability/(Flexibility*Caliper)
The Dryness Index is a reflection of one of the unexpected interactions that an absorbent article, particularly a sanitary napkin needs to satisfy, in order to provide overall dryness and/or comfort benefits to the wearer of the product. The dryness index reflects that perceived wetness in use is determined by both the dryness of the wearer facing surface of the product that lies closest to the body in use (i.e. absorbent article rewet test) and the dryness that can be achieved via water vapour exchange with the environment and air circulation via the backsheet (i.e. effective breathability).
The effective breathability is determined from the equation below:
xe2x80x83Effective Breathability=Vapour Permeability+0.25xc3x97Air Permeability
The effective breathability determines a numerical value for the breathability. It considers the two key mechanisms that are likely to participate in exchange of humidity and temperature while wearing a absorbent article having a breathable backsheet. The first mechanism is water vapour exchange via the process of diffusion. This is a continuous process and the mechanism is well understood and represented by a simple diffusion equation. In addition, body motion can result in a change in the relative position of the wearer""s body and the absorbent article, for example between a sanitary article and the body known as gapping. This motion also is accompanied by a process of air exchange. Repetitive bodily motion can quite literally pump air into and out of the backsheet or at the sides of the product, where a product may not maintain intimate contact to the body. Naturally the stiffer an absorbent article is in the genital region the less likely is this process of pumping to deliver an additional benefit to simple vapour exchange since the product is less deformable and is likely to press up closer to the body like a gasket.
The dryness index provides an indication of the ability of the article to absorb fluids and thus provide protection to the consumer which is given as a function of the permeability of the article and the overall product dryness.
The Sensory Index is an index that quantifies the relationship between product attributes that need to be satisfied in addition to breathability to deliver a true benefit in use. This is due the cross interactions between unexpected product design elements; namely breathability, the product caliper and product stiffness/flexibility.
Thus in short, the sensory index values gives an indication of the range of values of the permeability, flexibility and caliper of the product according to the present invention which provides protection and comfort benefits.
According to the present invention the absorbent article has a sensory index of greater than 50, preferably greater than 100, more preferably greater than 200, most preferably greater than 300. The article further has a dryness index of greater than 0.5, preferably greater than 2.0, more preferably greater than 4, most preferably greater than 10.
A further aspect of the present invention relates to the joining of the topsheet, backsheet and absorbent core elements to provide the absorbent article. According to the present invention at least two, preferably all, of the elements of the article are joined.
Each of said elements comprises at least one layer having a wearer facing surface and a garment facing surface. Typically, adjacent garment facing surfaces form a common interface with the wearer facing surface of an adjacent element or layer. The elements or layers are joined together across this common interface. In this manner the topsheet is joined to the absorbent core, and the core is joined to the backsheet. Furthermore, each of said topsheet, backsheet and core elements may comprise more than one layer and these layers may also be similarly joined. In addition the topsheet may be directly or indirectly joined to the backsheet at the periphery of the absorbent article.
The elements and layers thereof may be joined by any means known in the art for affixing two adjacent layers of material, such that the layers are directly attached to one another or directly attached to one another via the joining means. Suitable joining means include adhesive, fusion bonding, ultra sonic bonding, stitching, heat (e.g. crimping), embossing, and/or pressure bonds, or dynamic mechanical bonds. According to an embodiment of the present invention the preferred means of joining is adhesive. Suitable adhesives include non pressure sensitive and cold adhesives. The adhesive may be applied by any means known in the art such as spiral application, slot coating, spraying, spiral spraying, curtain coating, control coating and printing, provided that the adhesive does not substantially affect the breathability.
In a preferred embodiment of the present invention the interelement or interlayer joining adhesive is selected and applied so as to reduce any impact it may have on the effective breathability of the absorbent article and preferably also the flexibility of the absorbent article. In this manner the dryness index and sensory index values may in fact have been increased. Since many commonly utilised adhesives are not vapour permeable it is highly preferable to minimise the amount of adhesive used to join the layers/elements of the absorbent article in order to minimise their impact on the permeability (breathability) and preferably also the flexibility of the absorbent article. One means of achieving this is to use particular adhesive application methods such as open adhesive application techniques, whereby areas of the common interface are adhesive free, whilst retaining the required level of attachment/joining of the two adjacent layers or elements. In particular spiral spraying is preferred. The layers and elements should be joined in such a manner so that the absorbent article product maintains structural integrity but no more. This method finds particular application for the interlayer joining of the backsheet element layers and the joining of the backsheet element and the absorbent core element. Alternatively adhesives which are vapour permeable may be used.
Preferably not more than 40%, more preferably less than 20%, most preferably less than 10% of the common interface of two adjacent layers or elements is joined. Furthermore, the density of the adhesive should be reduced and a thin application of adhesive is preferred.
In a preferred embodiment of the present invention wherein the absorbent article finds utility as a sanitary napkin or panty liner, the absorbent article is also provided with a panty fastening means which provides means to attach the article to an undergarment. For example the panty fastening means may comprise a mechanical fastener such as hook and loop fasteners such as marketed under the tradename VELCRO, snaps or holders. Alternatively, the article is fastened to the undergarment by means of panty fastening adhesive on the backsheet. The panty fastening adhesive provides a means for securing the article to the panty and preferably a means for securing the article when soiled, to the fold and wrap package for convenient disposal. Typically, at least a portion of the garment facing surface of the backsheet is coated with adhesive to form the panty fastening adhesive. Any adhesive or glue used in the art for such purposes can be used for the panty fastening adhesive herein. Pressure sensitive adhesives are most preferred. Suitable adhesives include Century A-305-IV manufactured by the Century Adhesives Corporation of Columbus, Ohio, and Instant LOK 34-2823 manufactured by the National Starch and Chemical Company of Bridgewater, N.J., 3 Sigma 3153 manufactured by 3 Sigma and Fuller H-2238ZP manufactured by the H.B. Fuller Co.
The panty fastening adhesive is typically applied to the backsheet by slot coating. In order to reduce the effect on the breathablility of the backsheet and thus of the article as a whole, the adhesive is preferably applied such that at least 60%, preferably from at least 80%, most preferably at least 90% of the surface of the backsheet is adhesive free. The required adhesiveness can still be achieved even when using reduced surface coverage by using a particular distribution such as thinner strips, discontinuous strips of adhesive, intermittent dots, random patterns spirals.
The panty fastening adhesive is typically covered with a removable release paper or film in order to prevent the adhesive from drying out or adhering to another surface other than the panty prior to use. Any commercially available release paper or film may be used. Suitable examples include BL 30MG-A SILOX EI/O and BL 30 MG-A SILOX 4 P/O available from Akrosil Corporation.
According to the present invention the absorbent article can be used beneficially in the context of sanitary napkins, panty liners, incontinence articles and diapers. However, sanitary napkins are particularly susceptible to the present invention. The disposable article may thus also have all those features and parts which are typical for products in the context of their intended use.
The topsheet retention test is utilized to assess the liquid retention character (of bodily discharges) of topsheet materials or composites that may be used on disposable absorbent articles and particularly sanitary napkins.
The basic principal of the test is to evaluate the liquid retention behaviour of alternative topsheet materials to liquids that simulate bodily discharges. A xe2x80x9cgood topsheet materialxe2x80x9d in this test can be a film (e.g. apertured formed film) or a fibrous or a fibrous nature film provided it has a low propensity to acquiring and retaining liquids either on or within its structure. Naturally a xe2x80x9cgood topsheetxe2x80x9d is also, in addition to having low retention properties, expected to allow rapid transmission of bodily discharges further into the article and to hinder discharges that are contained within the article from returning to the upper (body side) surface of the article. Additionally a xe2x80x9cgood topsheetxe2x80x9d should also maintain a clean appearance during use of the articles.
To assess the topsheets"" retention to liquid, a test is performed as detailed below:
Two sheets (with dimensions of 5 cmxc3x975 cm) of a commercially available airlayed absorbent tissue each with a basis weight of 63 g/m2 available from Walkisoft USA under the supplier code Metmar (P50W.IPED) are utilised to simulate an absorbent core.
A sample of the topsheet material (with dimensions of 5 cmxc3x975 cm) that is to be assessed is placed directly on top of this absorbent structure. A standardised test liquid closely matching menses in viscosity and electrical conductivity (see below) is dripped onto the centre of the test sample from a height of 3 cm and at a rate of 2 g/min. until a total of 2 grams has been introduced onto the sample. The sample is left without further interference for a period of 1 minute.
Following the 1 min. waiting period a PERSPEX block (1 cm thick with dimensions 8.5 cmxc3x978.5 cm) is placed on top of the test sample and a weight is lower gently onto the total assemble for a period of 5 minutes. The total pressure exerted onto the test sample, at this point, is 70 g/cm2.
The weight and PERSPEX block is removed and carefully the topsheet sample is removed and placed on a stack of 2 sheets (with dimensions 12 cmxc3x9712 cm) of commercially available filter/blotting paper {produced by Cartiera Favini S.p.A. Italy; Type Abssorbente Bianca xe2x80x9cN30xe2x80x9d (local vendor Ditta Bragiola SpA. Perugia, Italy)} that have been pre-weighed. A second stack of 2 pre-weighed filter papers are placed on top of the topsheet sample. A second weight is placed on top of the filter paper stack containing the topsheet sample. The second weight exerts a pressure onto the filter paper stack of 130 g/cm2 for a period of 15 second. The weight (for this critical step) is attached to a hydraulic arm. The lowering of the weight and time the sample is placed under pressure is controlled via a simple electronic device to ensure reproduceability from one test to the next.
The second weight is removed and each (lying above and below the topsheet sample) filter paper stack is weighed and the difference for each surface (liquid pick-up from the topsheet sample) recorded. Materials that have a zero pick-up value for the top surface (placed normally in contact with the user""s skin) are given a zero xe2x80x9ctopsheet retentionxe2x80x9d value independent of having a non-zero value for the bottom surface as these materials clearly demonstrate non-communication between the upper and lower surfaces.
The test solution PIF is a widely used test liquid in the paper industry due to its simple composition, ability to be prepared and maintain high standards of solution quality and its similarity to human menses with respect to viscosity and ionic surface tension.
The solution PIF is prepared by dissolving the following reagent components, at the indicated quantities, into 1 liter of distilled water. Care should be taken in dissolving the solid components and particularly the Carboxylmethyl-cellulose. Typically the solid components should be added over a period of one hour slowly and with constant stirring of the solution (via a magnetic stirring device).
Supplier Sigma Chemicals, USA
Representative topsheet samples commonly used in hygienic articles and available from a range of companies have been tested and the results are detailed in the attached Table.
The air permeability test is utilized to assess the ability of the absorbent core to exchange/circulate vapour and preferably air and is carried out on the core material as detailed for an absorbent article.
The air/vapour permeability of representative examples of absorbent core elements has been assessed. The absorbent core have been manufactured under normal manufacturing procedures by P and G Pescara Technical Centre (Italy) or removed from available market products.